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 $69.57   3.343%   $71.8957   $71.90   $71.90   $71.90  
  Purchase #2 $182.81   11.217%   $203.3158   $203.32   $203.30   $203.30  
  Purchase #3 $246.50   3.142%   $254.245   $254.25   $254.25   $254.20  
  Purchase #4 $66.32   4.166%   $69.0829   $69.08   $69.10   $69.10  
  Purchase #5 $139.39   12.313%   $156.5531   $156.55   $156.55   $156.60  
  Purchase #6 $44.46   7.232%   $47.6753   $47.68   $47.70   $47.70  
  Purchase #7 $191.97   13.832%   $218.5233   $218.52   $218.50   $218.50  
  7 purchase totals = $941.02       $1,021.2911   $1,021.30   $1,021.30   $1,021.30