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 $67.51   12.373%   $75.863   $75.86   $75.85   $75.90  
  Purchase #2 $16.84   13.106%   $19.0471   $19.05   $19.05   $19.00  
  Purchase #3 $173.31   4.625%   $181.3256   $181.33   $181.35   $181.30  
  Purchase #4 $152.74   7.282%   $163.8625   $163.86   $163.85   $163.90  
  Purchase #5 $66.44   8.561%   $72.1279   $72.13   $72.15   $72.10  
  Purchase #6 $45.76   11.585%   $51.0613   $51.06   $51.05   $51.10  
  Purchase #7 $235.52   8.135%   $254.6796   $254.68   $254.70   $254.70  
  7 purchase totals = $758.12       $817.9670   $817.97   $818.00   $818.00