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 $42.96   3.401%   $44.4211   $44.42   $44.40   $44.40  
  Purchase #2 $119.76   12.736%   $135.0126   $135.01   $135.00   $135.00  
  Purchase #3 $59.88   9.617%   $65.6387   $65.64   $65.65   $65.60  
  Purchase #4 $165.59   3.316%   $171.081   $171.08   $171.10   $171.10  
  Purchase #5 $116.50   8.390%   $126.2744   $126.27   $126.25   $126.30  
  Purchase #6 $227.46   7.487%   $244.4899   $244.49   $244.50   $244.50  
  Purchase #7 $243.96   8.344%   $264.316   $264.32   $264.30   $264.30  
  7 purchase totals = $976.11       $1,051.2337   $1,051.23   $1,051.20   $1,051.20