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 $75.35   11.750%   $84.2036   $84.20   $84.20   $84.20  
  Purchase #2 $11.45   4.744%   $11.9932   $11.99   $12.00   $12.00  
  Purchase #3 $168.45   13.336%   $190.9145   $190.91   $190.90   $190.90  
  Purchase #4 $228.58   11.130%   $254.021   $254.02   $254.00   $254.00  
  Purchase #5 $134.53   11.729%   $150.309   $150.31   $150.30   $150.30  
  Purchase #6 $241.73   5.816%   $255.789   $255.79   $255.80   $255.80  
  Purchase #7 $211.94   7.653%   $228.1598   $228.16   $228.15   $228.20  
  7 purchase totals = $1,072.03       $1,175.3901   $1,175.38   $1,175.35   $1,175.40