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 $101.76   8.700%   $110.6131   $110.61   $110.60   $110.60  
  Purchase #2 $182.29   11.430%   $203.1257   $203.13   $203.15   $203.10  
  Purchase #3 $171.96   12.830%   $194.0225   $194.02   $194.00   $194.00  
  Purchase #4 $216.90   11.336%   $241.4878   $241.49   $241.50   $241.50  
  Purchase #5 $197.31   10.508%   $218.0433   $218.04   $218.05   $218.00  
  Purchase #6 $193.64   7.442%   $208.0507   $208.05   $208.05   $208.10  
  Purchase #7 $61.75   7.296%   $66.2553   $66.26   $66.25   $66.30  
  7 purchase totals = $1,125.61       $1,241.5984   $1,241.60   $1,241.60   $1,241.60