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 $96.44   8.190%   $104.3384   $104.34   $104.35   $104.30  
  Purchase #2 $50.55   4.753%   $52.9526   $52.95   $52.95   $53.00  
  Purchase #3 $52.59   3.375%   $54.3649   $54.36   $54.35   $54.40  
  Purchase #4 $243.30   8.655%   $264.3576   $264.36   $264.35   $264.40  
  Purchase #5 $126.85   6.817%   $135.4974   $135.50   $135.50   $135.50  
  Purchase #6 $178.92   10.574%   $197.839   $197.84   $197.85   $197.80  
  Purchase #7 $61.66   5.420%   $65.002   $65.00   $65.00   $65.00  
  7 purchase totals = $810.31       $874.3519   $874.35   $874.35   $874.40