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 $49.46   6.598%   $52.7234   $52.72   $52.70   $52.70  
  Purchase #2 $205.53   5.330%   $216.4847   $216.48   $216.50   $216.50  
  Purchase #3 $183.63   5.559%   $193.838   $193.84   $193.85   $193.80  
  Purchase #4 $98.31   4.279%   $102.5167   $102.52   $102.50   $102.50  
  Purchase #5 $116.58   8.487%   $126.4741   $126.47   $126.45   $126.50  
  Purchase #6 $86.33   4.229%   $89.9809   $89.98   $90.00   $90.00  
  Purchase #7 $87.94   12.561%   $98.9861   $98.99   $99.00   $99.00  
  7 purchase totals = $827.78       $881.0039   $881.00   $881.00   $881.00