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 $64.98   12.682%   $73.2208   $73.22   $73.20   $73.20  
  Purchase #2 $150.94   13.536%   $171.3712   $171.37   $171.35   $171.40  
  Purchase #3 $223.35   12.180%   $250.554   $250.55   $250.55   $250.60  
  Purchase #4 $197.88   11.173%   $219.9891   $219.99   $220.00   $220.00  
  Purchase #5 $91.84   7.566%   $98.7886   $98.79   $98.80   $98.80  
  Purchase #6 $222.93   8.345%   $241.5335   $241.53   $241.55   $241.50  
  Purchase #7 $183.74   12.571%   $206.838   $206.84   $206.85   $206.80  
  7 purchase totals = $1,135.66       $1,262.2952   $1,262.29   $1,262.30   $1,262.30