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 $76.96   10.832%   $85.2963   $85.30   $85.30   $85.30  
  Purchase #2 $104.31   11.303%   $116.1002   $116.10   $116.10   $116.10  
  Purchase #3 $154.25   6.108%   $163.6716   $163.67   $163.65   $163.70  
  Purchase #4 $92.61   11.164%   $102.949   $102.95   $102.95   $102.90  
  Purchase #5 $189.93   7.273%   $203.7436   $203.74   $203.75   $203.70  
  Purchase #6 $223.53   5.230%   $235.2206   $235.22   $235.20   $235.20  
  Purchase #7 $97.59   3.874%   $101.3706   $101.37   $101.35   $101.40  
  7 purchase totals = $939.18       $1,008.3519   $1,008.35   $1,008.30   $1,008.30