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 $172.95   12.720%   $194.9492   $194.95   $194.95   $194.90  
  Purchase #2 $238.94   10.496%   $264.0191   $264.02   $264.00   $264.00  
  Purchase #3 $11.32   13.336%   $12.8296   $12.83   $12.85   $12.80  
  Purchase #4 $23.89   10.525%   $26.4044   $26.40   $26.40   $26.40  
  Purchase #5 $150.84   5.190%   $158.6686   $158.67   $158.65   $158.70  
  Purchase #6 $153.52   13.221%   $173.8169   $173.82   $173.80   $173.80  
  Purchase #7 $225.52   7.367%   $242.1341   $242.13   $242.15   $242.10  
  7 purchase totals = $976.98       $1,072.8219   $1,072.82   $1,072.80   $1,072.70