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 $65.80   13.146%   $74.4501   $74.45   $74.45   $74.50  
  Purchase #2 $89.73   8.478%   $97.3373   $97.34   $97.35   $97.30  
  Purchase #3 $100.75   5.232%   $106.0212   $106.02   $106.00   $106.00  
  Purchase #4 $195.32   8.834%   $212.5746   $212.57   $212.55   $212.60  
  Purchase #5 $197.52   7.761%   $212.8495   $212.85   $212.85   $212.80  
  Purchase #6 $205.96   11.499%   $229.6433   $229.64   $229.65   $229.60  
  Purchase #7 $23.64   3.155%   $24.3858   $24.39   $24.40   $24.40  
  7 purchase totals = $878.72       $957.2618   $957.26   $957.25   $957.20