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 $84.53   7.713%   $91.0498   $91.05   $91.05   $91.00  
  Purchase #2 $85.58   7.871%   $92.316   $92.32   $92.30   $92.30  
  Purchase #3 $154.28   9.530%   $168.9829   $168.98   $169.00   $169.00  
  Purchase #4 $139.55   9.873%   $153.3278   $153.33   $153.35   $153.30  
  Purchase #5 $165.50   6.258%   $175.857   $175.86   $175.85   $175.90  
  Purchase #6 $196.77   11.192%   $218.7925   $218.79   $218.80   $218.80  
  Purchase #7 $15.32   8.255%   $16.5847   $16.58   $16.60   $16.60  
  7 purchase totals = $841.53       $916.9107   $916.91   $916.95   $916.90