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 $98.34   13.184%   $111.3051   $111.31   $111.30   $111.30  
  Purchase #2 $219.79   4.309%   $229.2608   $229.26   $229.25   $229.30  
  Purchase #3 $244.72   12.816%   $276.0833   $276.08   $276.10   $276.10  
  Purchase #4 $236.57   11.797%   $264.4782   $264.48   $264.50   $264.50  
  Purchase #5 $166.72   12.512%   $187.58   $187.58   $187.60   $187.60  
  Purchase #6 $191.46   5.457%   $201.908   $201.91   $201.90   $201.90  
  Purchase #7 $117.52   9.216%   $128.3506   $128.35   $128.35   $128.40  
  7 purchase totals = $1,275.12       $1,398.9660   $1,398.97   $1,399.00   $1,399.10