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 $84.35   11.764%   $94.2729   $94.27   $94.25   $94.30  
  Purchase #2 $114.89   11.292%   $127.8634   $127.86   $127.85   $127.90  
  Purchase #3 $160.75   3.235%   $165.9503   $165.95   $165.95   $166.00  
  Purchase #4 $120.63   8.425%   $130.7931   $130.79   $130.80   $130.80  
  Purchase #5 $203.82   8.520%   $221.1855   $221.19   $221.20   $221.20  
  Purchase #6 $241.53   12.731%   $272.2792   $272.28   $272.30   $272.30  
  Purchase #7 $94.54   12.338%   $106.2043   $106.20   $106.20   $106.20  
  7 purchase totals = $1,020.51       $1,118.5487   $1,118.54   $1,118.55   $1,118.70