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 $102.52   12.121%   $114.9464   $114.95   $114.95   $114.90  
  Purchase #2 $57.85   12.437%   $65.0448   $65.04   $65.05   $65.00  
  Purchase #3 $47.65   4.400%   $49.7466   $49.75   $49.75   $49.70  
  Purchase #4 $232.41   6.212%   $246.8473   $246.85   $246.85   $246.80  
  Purchase #5 $126.80   4.778%   $132.8585   $132.86   $132.85   $132.90  
  Purchase #6 $177.98   7.638%   $191.5741   $191.57   $191.55   $191.60  
  Purchase #7 $63.86   12.842%   $72.0609   $72.06   $72.05   $72.10  
  7 purchase totals = $809.07       $873.0786   $873.08   $873.05   $873.00