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 $202.93   12.363%   $228.0182   $228.02   $228.00   $228.00  
  Purchase #2 $193.47   10.386%   $213.5638   $213.56   $213.55   $213.60  
  Purchase #3 $68.84   5.398%   $72.556   $72.56   $72.55   $72.60  
  Purchase #4 $108.25   12.381%   $121.6524   $121.65   $121.65   $121.70  
  Purchase #5 $99.26   10.469%   $109.6515   $109.65   $109.65   $109.70  
  Purchase #6 $55.77   4.644%   $58.36   $58.36   $58.35   $58.40  
  Purchase #7 $228.52   7.693%   $246.1   $246.10   $246.10   $246.10  
  7 purchase totals = $957.04       $1,049.9019   $1,049.90   $1,049.85   $1,050.10