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 $165.93   5.327%   $174.7691   $174.77   $174.75   $174.80  
  Purchase #2 $240.57   8.299%   $260.5349   $260.53   $260.55   $260.50  
  Purchase #3 $190.25   11.374%   $211.889   $211.89   $211.90   $211.90  
  Purchase #4 $172.76   6.826%   $184.5526   $184.55   $184.55   $184.60  
  Purchase #5 $229.71   11.311%   $255.6925   $255.69   $255.70   $255.70  
  Purchase #6 $192.52   5.363%   $202.8448   $202.84   $202.85   $202.80  
  Purchase #7 $25.90   4.211%   $26.9906   $26.99   $27.00   $27.00  
  7 purchase totals = $1,217.64       $1,317.2735   $1,317.26   $1,317.30   $1,317.30