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 $63.65   3.447%   $65.844   $65.84   $65.85   $65.80  
  Purchase #2 $162.34   4.161%   $169.095   $169.10   $169.10   $169.10  
  Purchase #3 $112.56   12.231%   $126.3272   $126.33   $126.35   $126.30  
  Purchase #4 $174.33   11.463%   $194.3134   $194.31   $194.30   $194.30  
  Purchase #5 $123.43   8.301%   $133.6759   $133.68   $133.70   $133.70  
  Purchase #6 $212.50   4.715%   $222.5194   $222.52   $222.50   $222.50  
  Purchase #7 $37.85   3.121%   $39.0313   $39.03   $39.05   $39.00  
  7 purchase totals = $886.66       $950.8062   $950.81   $950.85   $950.70