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 $52.70   10.809%   $58.3963   $58.40   $58.40   $58.40  
  Purchase #2 $167.85   9.632%   $184.0173   $184.02   $184.00   $184.00  
  Purchase #3 $211.83   11.454%   $236.093   $236.09   $236.10   $236.10  
  Purchase #4 $118.59   5.790%   $125.4564   $125.46   $125.45   $125.50  
  Purchase #5 $24.70   6.586%   $26.3267   $26.33   $26.35   $26.30  
  Purchase #6 $240.59   12.275%   $270.1224   $270.12   $270.10   $270.10  
  Purchase #7 $231.51   10.246%   $255.2305   $255.23   $255.25   $255.20  
  7 purchase totals = $1,047.77       $1,155.6426   $1,155.65   $1,155.65   $1,155.60