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 $91.84   7.219%   $98.4699   $98.47   $98.45   $98.50  
  Purchase #2 $177.62   12.798%   $200.3518   $200.35   $200.35   $200.40  
  Purchase #3 $37.80   4.637%   $39.5528   $39.55   $39.55   $39.60  
  Purchase #4 $248.56   4.264%   $259.1586   $259.16   $259.15   $259.20  
  Purchase #5 $110.94   9.445%   $121.4183   $121.42   $121.40   $121.40  
  Purchase #6 $62.35   4.449%   $65.124   $65.12   $65.10   $65.10  
  Purchase #7 $142.68   5.186%   $150.0794   $150.08   $150.10   $150.10  
  7 purchase totals = $871.79       $934.1548   $934.15   $934.10   $934.30