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 $58.57   12.256%   $65.7483   $65.75   $65.75   $65.70  
  Purchase #2 $190.34   11.818%   $212.8344   $212.83   $212.85   $212.80  
  Purchase #3 $225.95   12.700%   $254.6457   $254.65   $254.65   $254.60  
  Purchase #4 $45.68   7.831%   $49.2572   $49.26   $49.25   $49.30  
  Purchase #5 $103.25   4.639%   $108.0398   $108.04   $108.05   $108.00  
  Purchase #6 $212.68   13.517%   $241.428   $241.43   $241.45   $241.40  
  Purchase #7 $230.48   5.668%   $243.5436   $243.54   $243.55   $243.50  
  7 purchase totals = $1,066.95       $1,175.4970   $1,175.50   $1,175.55   $1,175.30