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 $241.72   9.305%   $264.212   $264.21   $264.20   $264.20  
  Purchase #2 $109.80   11.129%   $122.0196   $122.02   $122.00   $122.00  
  Purchase #3 $180.59   7.125%   $193.457   $193.46   $193.45   $193.50  
  Purchase #4 $97.66   7.430%   $104.9161   $104.92   $104.90   $104.90  
  Purchase #5 $110.35   4.637%   $115.4669   $115.47   $115.45   $115.50  
  Purchase #6 $147.30   11.463%   $164.185   $164.19   $164.20   $164.20  
  Purchase #7 $173.44   10.300%   $191.3043   $191.30   $191.30   $191.30  
  7 purchase totals = $1,060.86       $1,155.5609   $1,155.57   $1,155.50   $1,155.60