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 $88.39   8.800%   $96.1683   $96.17   $96.15   $96.20  
  Purchase #2 $232.49   8.198%   $251.5495   $251.55   $251.55   $251.50  
  Purchase #3 $50.93   7.306%   $54.6509   $54.65   $54.65   $54.70  
  Purchase #4 $159.30   12.863%   $179.7908   $179.79   $179.80   $179.80  
  Purchase #5 $249.38   5.492%   $263.0759   $263.08   $263.10   $263.10  
  Purchase #6 $236.51   3.631%   $245.0977   $245.10   $245.10   $245.10  
  Purchase #7 $135.26   11.430%   $150.7202   $150.72   $150.70   $150.70  
  7 purchase totals = $1,152.26       $1,241.0533   $1,241.06   $1,241.05   $1,241.10