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 $212.97   6.587%   $226.9983   $227.00   $227.00   $227.00  
  Purchase #2 $144.53   10.219%   $159.2995   $159.30   $159.30   $159.30  
  Purchase #3 $51.54   12.591%   $58.0294   $58.03   $58.05   $58.00  
  Purchase #4 $212.31   12.372%   $238.577   $238.58   $238.60   $238.60  
  Purchase #5 $231.65   6.183%   $245.9729   $245.97   $245.95   $246.00  
  Purchase #6 $80.78   10.624%   $89.3621   $89.36   $89.35   $89.40  
  Purchase #7 $123.88   8.324%   $134.1918   $134.19   $134.20   $134.20  
  7 purchase totals = $1,057.66       $1,152.4310   $1,152.43   $1,152.45   $1,152.50