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 $92.92   5.303%   $97.8475   $97.85   $97.85   $97.80  
  Purchase #2 $211.47   10.728%   $234.1565   $234.16   $234.15   $234.20  
  Purchase #3 $82.64   5.309%   $87.0274   $87.03   $87.05   $87.00  
  Purchase #4 $210.60   7.205%   $225.7737   $225.77   $225.75   $225.80  
  Purchase #5 $26.50   7.493%   $28.4856   $28.49   $28.50   $28.50  
  Purchase #6 $70.55   5.747%   $74.6045   $74.60   $74.60   $74.60  
  Purchase #7 $166.99   6.764%   $178.2852   $178.29   $178.30   $178.30  
  7 purchase totals = $861.67       $926.1804   $926.19   $926.20   $926.20