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 $104.33   6.352%   $110.957   $110.96   $110.95   $111.00  
  Purchase #2 $199.49   13.342%   $226.106   $226.11   $226.10   $226.10  
  Purchase #3 $94.59   12.438%   $106.3551   $106.36   $106.35   $106.40  
  Purchase #4 $123.62   11.652%   $138.0242   $138.02   $138.00   $138.00  
  Purchase #5 $210.36   5.825%   $222.6135   $222.61   $222.60   $222.60  
  Purchase #6 $80.72   12.696%   $90.9682   $90.97   $90.95   $91.00  
  Purchase #7 $154.97   10.663%   $171.4945   $171.49   $171.50   $171.50  
  7 purchase totals = $968.08       $1,066.5185   $1,066.52   $1,066.45   $1,066.60