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 $75.67   11.707%   $84.5287   $84.53   $84.55   $84.50  
  Purchase #2 $39.52   6.641%   $42.1445   $42.14   $42.15   $42.10  
  Purchase #3 $212.72   5.676%   $224.794   $224.79   $224.80   $224.80  
  Purchase #4 $35.95   3.472%   $37.1982   $37.20   $37.20   $37.20  
  Purchase #5 $180.68   12.355%   $203.003   $203.00   $203.00   $203.00  
  Purchase #6 $217.78   6.153%   $231.18   $231.18   $231.20   $231.20  
  Purchase #7 $96.88   10.191%   $106.753   $106.75   $106.75   $106.80  
  7 purchase totals = $859.20       $929.6014   $929.59   $929.65   $929.60