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 $68.30   11.439%   $76.1128   $76.11   $76.10   $76.10  
  Purchase #2 $61.29   12.156%   $68.7404   $68.74   $68.75   $68.70  
  Purchase #3 $216.68   6.188%   $230.0882   $230.09   $230.10   $230.10  
  Purchase #4 $136.88   9.794%   $150.286   $150.29   $150.30   $150.30  
  Purchase #5 $104.29   8.762%   $113.4279   $113.43   $113.45   $113.40  
  Purchase #6 $126.62   10.187%   $139.5188   $139.52   $139.50   $139.50  
  Purchase #7 $211.97   10.865%   $235.0005   $235.00   $235.00   $235.00  
  7 purchase totals = $926.03       $1,013.1746   $1,013.18   $1,013.20   $1,013.10