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 $111.68   11.611%   $124.6472   $124.65   $124.65   $124.60  
  Purchase #2 $204.32   9.313%   $223.3483   $223.35   $223.35   $223.30  
  Purchase #3 $53.70   8.517%   $58.2736   $58.27   $58.25   $58.30  
  Purchase #4 $80.65   5.550%   $85.1261   $85.13   $85.15   $85.10  
  Purchase #5 $149.31   7.353%   $160.2888   $160.29   $160.30   $160.30  
  Purchase #6 $95.51   11.751%   $106.7334   $106.73   $106.75   $106.70  
  Purchase #7 $27.59   6.192%   $29.2984   $29.30   $29.30   $29.30  
  7 purchase totals = $722.76       $787.7158   $787.72   $787.75   $787.60