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 $218.33   11.749%   $243.9816   $243.98   $244.00   $244.00  
  Purchase #2 $130.27   13.582%   $147.9633   $147.96   $147.95   $148.00  
  Purchase #3 $204.52   12.284%   $229.6432   $229.64   $229.65   $229.60  
  Purchase #4 $92.93   3.363%   $96.0552   $96.06   $96.05   $96.10  
  Purchase #5 $130.79   4.452%   $136.6128   $136.61   $136.60   $136.60  
  Purchase #6 $212.65   5.346%   $224.0183   $224.02   $224.00   $224.00  
  Purchase #7 $142.76   8.267%   $154.562   $154.56   $154.55   $154.60  
  7 purchase totals = $1,132.25       $1,232.8364   $1,232.83   $1,232.80   $1,232.90