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 $113.91   3.860%   $118.3069   $118.31   $118.30   $118.30  
  Purchase #2 $201.38   4.386%   $210.2125   $210.21   $210.20   $210.20  
  Purchase #3 $182.87   11.581%   $204.0482   $204.05   $204.05   $204.00  
  Purchase #4 $179.28   7.377%   $192.5055   $192.51   $192.50   $192.50  
  Purchase #5 $35.78   3.413%   $37.0012   $37.00   $37.00   $37.00  
  Purchase #6 $57.41   6.371%   $61.0676   $61.07   $61.05   $61.10  
  Purchase #7 $216.27   12.442%   $243.1783   $243.18   $243.20   $243.20  
  7 purchase totals = $986.90       $1,066.3202   $1,066.33   $1,066.30   $1,066.30