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 $32.85   12.532%   $36.9668   $36.97   $36.95   $37.00  
  Purchase #2 $238.65   10.739%   $264.2786   $264.28   $264.30   $264.30  
  Purchase #3 $174.26   5.478%   $183.806   $183.81   $183.80   $183.80  
  Purchase #4 $183.74   10.779%   $203.5453   $203.55   $203.55   $203.50  
  Purchase #5 $57.50   4.217%   $59.9248   $59.92   $59.90   $59.90  
  Purchase #6 $10.25   5.175%   $10.7804   $10.78   $10.80   $10.80  
  Purchase #7 $186.65   7.701%   $201.0239   $201.02   $201.00   $201.00  
  7 purchase totals = $883.90       $960.3258   $960.33   $960.30   $960.30