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 $87.83   7.241%   $94.1898   $94.19   $94.20   $94.20  
  Purchase #2 $240.93   10.169%   $265.4302   $265.43   $265.45   $265.40  
  Purchase #3 $22.57   13.197%   $25.5486   $25.55   $25.55   $25.50  
  Purchase #4 $74.34   3.840%   $77.1947   $77.19   $77.20   $77.20  
  Purchase #5 $236.36   13.525%   $268.3277   $268.33   $268.35   $268.30  
  Purchase #6 $37.60   11.524%   $41.933   $41.93   $41.95   $41.90  
  Purchase #7 $93.65   3.173%   $96.6215   $96.62   $96.60   $96.60  
  7 purchase totals = $793.28       $869.2455   $869.24   $869.30   $869.10