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 $217.99   3.756%   $226.1777   $226.18   $226.20   $226.20  
  Purchase #2 $100.89   3.745%   $104.6683   $104.67   $104.65   $104.70  
  Purchase #3 $244.87   12.108%   $274.5189   $274.52   $274.50   $274.50  
  Purchase #4 $198.29   11.214%   $220.5262   $220.53   $220.55   $220.50  
  Purchase #5 $102.85   12.530%   $115.7371   $115.74   $115.75   $115.70  
  Purchase #6 $54.77   7.717%   $58.9966   $59.00   $59.00   $59.00  
  Purchase #7 $161.82   3.751%   $167.8899   $167.89   $167.90   $167.90  
  7 purchase totals = $1,081.48       $1,168.5147   $1,168.53   $1,168.55   $1,168.50