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 $116.65   12.826%   $131.6115   $131.61   $131.60   $131.60  
  Purchase #2 $208.85   12.572%   $235.1066   $235.11   $235.10   $235.10  
  Purchase #3 $220.76   6.580%   $235.286   $235.29   $235.30   $235.30  
  Purchase #4 $95.44   4.140%   $99.3912   $99.39   $99.40   $99.40  
  Purchase #5 $178.55   10.717%   $197.6852   $197.69   $197.70   $197.70  
  Purchase #6 $68.99   12.220%   $77.4206   $77.42   $77.40   $77.40  
  Purchase #7 $87.33   10.608%   $96.594   $96.59   $96.60   $96.60  
  7 purchase totals = $976.57       $1,073.0951   $1,073.10   $1,073.10   $1,073.10