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 $148.99   11.139%   $165.586   $165.59   $165.60   $165.60  
  Purchase #2 $92.87   3.632%   $96.243   $96.24   $96.25   $96.20  
  Purchase #3 $69.33   10.835%   $76.8419   $76.84   $76.85   $76.80  
  Purchase #4 $104.68   5.278%   $110.205   $110.21   $110.20   $110.20  
  Purchase #5 $64.52   10.350%   $71.1978   $71.20   $71.20   $71.20  
  Purchase #6 $247.48   12.191%   $277.6503   $277.65   $277.65   $277.70  
  Purchase #7 $198.26   10.792%   $219.6562   $219.66   $219.65   $219.70  
  7 purchase totals = $926.13       $1,017.3802   $1,017.39   $1,017.40   $1,017.40