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 $62.34   4.221%   $64.9714   $64.97   $64.95   $65.00  
  Purchase #2 $226.83   12.563%   $255.3267   $255.33   $255.35   $255.30  
  Purchase #3 $20.94   3.614%   $21.6968   $21.70   $21.70   $21.70  
  Purchase #4 $180.56   10.300%   $199.1577   $199.16   $199.15   $199.20  
  Purchase #5 $46.30   12.737%   $52.1972   $52.20   $52.20   $52.20  
  Purchase #6 $192.91   6.157%   $204.7875   $204.79   $204.80   $204.80  
  Purchase #7 $235.44   12.711%   $265.3668   $265.37   $265.35   $265.40  
  7 purchase totals = $965.32       $1,063.5041   $1,063.52   $1,063.50   $1,063.60