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 $68.82   11.463%   $76.7088   $76.71   $76.70   $76.70  
  Purchase #2 $80.43   5.650%   $84.9743   $84.97   $84.95   $85.00  
  Purchase #3 $10.85   5.343%   $11.4297   $11.43   $11.45   $11.40  
  Purchase #4 $95.52   10.268%   $105.328   $105.33   $105.35   $105.30  
  Purchase #5 $160.67   4.483%   $167.8728   $167.87   $167.85   $167.90  
  Purchase #6 $99.30   5.107%   $104.3713   $104.37   $104.35   $104.40  
  Purchase #7 $141.60   12.289%   $159.0012   $159.00   $159.00   $159.00  
  7 purchase totals = $657.19       $709.6861   $709.68   $709.65   $709.70