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 $49.27   3.513%   $51.0009   $51.00   $51.00   $51.00  
  Purchase #2 $192.79   3.315%   $199.181   $199.18   $199.20   $199.20  
  Purchase #3 $202.35   13.461%   $229.5883   $229.59   $229.60   $229.60  
  Purchase #4 $69.80   5.787%   $73.8393   $73.84   $73.85   $73.80  
  Purchase #5 $58.64   12.282%   $65.8422   $65.84   $65.85   $65.80  
  Purchase #6 $156.58   10.559%   $173.1133   $173.11   $173.10   $173.10  
  Purchase #7 $235.37   6.481%   $250.6243   $250.62   $250.60   $250.60  
  7 purchase totals = $964.80       $1,043.1893   $1,043.18   $1,043.20   $1,043.10