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 $57.52   4.822%   $60.2936   $60.29   $60.30   $60.30  
  Purchase #2 $151.36   12.104%   $169.6806   $169.68   $169.70   $169.70  
  Purchase #3 $95.52   13.854%   $108.7533   $108.75   $108.75   $108.80  
  Purchase #4 $148.83   4.709%   $155.8384   $155.84   $155.85   $155.80  
  Purchase #5 $64.37   8.340%   $69.7385   $69.74   $69.75   $69.70  
  Purchase #6 $181.94   4.144%   $189.4796   $189.48   $189.50   $189.50  
  Purchase #7 $216.68   13.759%   $246.493   $246.49   $246.50   $246.50  
  7 purchase totals = $916.22       $1,000.2770   $1,000.27   $1,000.35   $1,000.30