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 $181.65   11.688%   $202.8813   $202.88   $202.90   $202.90  
  Purchase #2 $56.39   10.279%   $62.1863   $62.19   $62.20   $62.20  
  Purchase #3 $108.29   9.872%   $118.9804   $118.98   $119.00   $119.00  
  Purchase #4 $202.59   12.362%   $227.6342   $227.63   $227.65   $227.60  
  Purchase #5 $113.81   10.369%   $125.611   $125.61   $125.60   $125.60  
  Purchase #6 $230.31   7.608%   $247.832   $247.83   $247.85   $247.80  
  Purchase #7 $28.30   10.764%   $31.3462   $31.35   $31.35   $31.30  
  7 purchase totals = $921.34       $1,016.4714   $1,016.47   $1,016.55   $1,016.40