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 $152.76   6.474%   $162.6497   $162.65   $162.65   $162.60  
  Purchase #2 $57.39   13.428%   $65.0963   $65.10   $65.10   $65.10  
  Purchase #3 $161.44   5.404%   $170.1642   $170.16   $170.15   $170.20  
  Purchase #4 $108.82   11.365%   $121.1874   $121.19   $121.20   $121.20  
  Purchase #5 $179.52   12.831%   $202.5542   $202.55   $202.55   $202.60  
  Purchase #6 $191.59   9.296%   $209.4002   $209.40   $209.40   $209.40  
  Purchase #7 $150.55   7.638%   $162.049   $162.05   $162.05   $162.00  
  7 purchase totals = $1,002.07       $1,093.1010   $1,093.10   $1,093.10   $1,093.10