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 $124.70   13.761%   $141.86   $141.86   $141.85   $141.90  
  Purchase #2 $48.70   7.570%   $52.3866   $52.39   $52.40   $52.40  
  Purchase #3 $107.67   12.684%   $121.3269   $121.33   $121.35   $121.30  
  Purchase #4 $249.68   13.698%   $283.8812   $283.88   $283.90   $283.90  
  Purchase #5 $203.99   11.141%   $226.7165   $226.72   $226.70   $226.70  
  Purchase #6 $206.32   12.180%   $231.4498   $231.45   $231.45   $231.40  
  Purchase #7 $51.73   4.754%   $54.1892   $54.19   $54.20   $54.20  
  7 purchase totals = $992.79       $1,111.8102   $1,111.82   $1,111.85   $1,111.80