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 $60.41   12.588%   $68.0144   $68.01   $68.00   $68.00  
  Purchase #2 $202.92   13.136%   $229.5756   $229.58   $229.60   $229.60  
  Purchase #3 $59.70   12.188%   $66.9762   $66.98   $67.00   $67.00  
  Purchase #4 $212.27   8.279%   $229.8438   $229.84   $229.85   $229.80  
  Purchase #5 $148.53   5.250%   $156.3278   $156.33   $156.35   $156.30  
  Purchase #6 $192.96   9.123%   $210.5637   $210.56   $210.55   $210.60  
  Purchase #7 $66.28   5.824%   $70.1401   $70.14   $70.15   $70.10  
  7 purchase totals = $943.07       $1,031.4416   $1,031.44   $1,031.50   $1,031.40