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 $86.38   6.444%   $91.9463   $91.95   $91.95   $91.90  
  Purchase #2 $108.79   7.283%   $116.7132   $116.71   $116.70   $116.70  
  Purchase #3 $216.73   12.237%   $243.2513   $243.25   $243.25   $243.30  
  Purchase #4 $222.80   3.849%   $231.3756   $231.38   $231.40   $231.40  
  Purchase #5 $83.62   5.362%   $88.1037   $88.10   $88.10   $88.10  
  Purchase #6 $61.53   9.482%   $67.3643   $67.36   $67.35   $67.40  
  Purchase #7 $196.59   7.819%   $211.9614   $211.96   $211.95   $212.00  
  7 purchase totals = $976.44       $1,050.7158   $1,050.71   $1,050.70   $1,050.80