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 $194.62   6.529%   $207.3267   $207.33   $207.35   $207.30  
  Purchase #2 $192.65   13.310%   $218.2917   $218.29   $218.30   $218.30  
  Purchase #3 $187.30   3.220%   $193.3311   $193.33   $193.35   $193.30  
  Purchase #4 $52.55   11.143%   $58.4056   $58.41   $58.40   $58.40  
  Purchase #5 $42.28   6.836%   $45.1703   $45.17   $45.15   $45.20  
  Purchase #6 $33.43   4.487%   $34.93   $34.93   $34.95   $34.90  
  Purchase #7 $164.31   3.776%   $170.5143   $170.51   $170.50   $170.50  
  7 purchase totals = $867.14       $927.9697   $927.97   $928.00   $927.90