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 $228.85   11.120%   $254.2981   $254.30   $254.30   $254.30  
  Purchase #2 $195.86   4.487%   $204.6482   $204.65   $204.65   $204.60  
  Purchase #3 $61.26   11.249%   $68.1511   $68.15   $68.15   $68.20  
  Purchase #4 $31.74   5.757%   $33.5673   $33.57   $33.55   $33.60  
  Purchase #5 $218.47   11.611%   $243.8366   $243.84   $243.85   $243.80  
  Purchase #6 $68.58   13.617%   $77.9185   $77.92   $77.90   $77.90  
  Purchase #7 $169.85   10.533%   $187.7403   $187.74   $187.75   $187.70  
  7 purchase totals = $974.61       $1,070.1601   $1,070.17   $1,070.15   $1,070.10