Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $232.44   10.627%   $257.1414   $257.14   $257.15   $257.10  
  Purchase #2 $215.38   6.621%   $229.6403   $229.64   $229.65   $229.60  
  Purchase #3 $79.36   13.749%   $90.2712   $90.27   $90.25   $90.30  
  Purchase #4 $127.52   10.873%   $141.3852   $141.39   $141.40   $141.40  
  Purchase #5 $227.44   11.850%   $254.3916   $254.39   $254.40   $254.40  
  Purchase #6 $124.26   11.706%   $138.8059   $138.81   $138.80   $138.80  
  Purchase #7 $240.84   6.693%   $256.9594   $256.96   $256.95   $257.00  
  7 purchase totals = $1,247.24       $1,368.5950   $1,368.60   $1,368.60   $1,368.60