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 $81.68   12.444%   $91.8443   $91.84   $91.85   $91.80  
  Purchase #2 $157.59   12.286%   $176.9515   $176.95   $176.95   $177.00  
  Purchase #3 $116.41   8.582%   $126.4003   $126.40   $126.40   $126.40  
  Purchase #4 $86.48   10.797%   $95.8172   $95.82   $95.80   $95.80  
  Purchase #5 $66.72   12.503%   $75.062   $75.06   $75.05   $75.10  
  Purchase #6 $167.78   8.426%   $181.9171   $181.92   $181.90   $181.90  
  Purchase #7 $80.60   5.544%   $85.0685   $85.07   $85.05   $85.10  
  7 purchase totals = $757.26       $833.0609   $833.06   $833.00   $833.10