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 $95.83   6.779%   $102.3263   $102.33   $102.35   $102.30  
  Purchase #2 $216.96   7.107%   $232.3793   $232.38   $232.40   $232.40  
  Purchase #3 $122.52   6.103%   $129.9974   $130.00   $130.00   $130.00  
  Purchase #4 $229.48   10.754%   $254.1583   $254.16   $254.15   $254.20  
  Purchase #5 $83.28   10.827%   $92.2967   $92.30   $92.30   $92.30  
  Purchase #6 $121.70   7.629%   $130.9845   $130.98   $131.00   $131.00  
  Purchase #7 $52.28   12.741%   $58.941   $58.94   $58.95   $58.90  
  7 purchase totals = $922.05       $1,001.0835   $1,001.09   $1,001.15   $1,001.10