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 $141.52   8.827%   $154.012   $154.01   $154.00   $154.00  
  Purchase #2 $170.59   12.115%   $191.257   $191.26   $191.25   $191.30  
  Purchase #3 $41.50   3.755%   $43.0583   $43.06   $43.05   $43.10  
  Purchase #4 $203.60   3.147%   $210.0073   $210.01   $210.00   $210.00  
  Purchase #5 $89.94   9.516%   $98.4987   $98.50   $98.50   $98.50  
  Purchase #6 $155.73   8.739%   $169.3392   $169.34   $169.35   $169.30  
  Purchase #7 $75.87   6.709%   $80.9601   $80.96   $80.95   $81.00  
  7 purchase totals = $878.75       $947.1326   $947.14   $947.10   $947.20