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 $14.79   11.603%   $16.5061   $16.51   $16.50   $16.50  
  Purchase #2 $87.55   8.869%   $95.3148   $95.31   $95.30   $95.30  
  Purchase #3 $33.85   3.800%   $35.1363   $35.14   $35.15   $35.10  
  Purchase #4 $173.84   12.201%   $195.0502   $195.05   $195.05   $195.10  
  Purchase #5 $119.29   5.755%   $126.1551   $126.16   $126.15   $126.20  
  Purchase #6 $180.64   12.411%   $203.0592   $203.06   $203.05   $203.10  
  Purchase #7 $157.80   4.832%   $165.4249   $165.42   $165.40   $165.40  
  7 purchase totals = $767.76       $836.6466   $836.65   $836.60   $836.70