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 $119.77   3.757%   $124.2698   $124.27   $124.25   $124.30  
  Purchase #2 $72.25   11.361%   $80.4583   $80.46   $80.45   $80.50  
  Purchase #3 $31.36   6.732%   $33.4712   $33.47   $33.45   $33.50  
  Purchase #4 $207.87   9.833%   $228.3099   $228.31   $228.30   $228.30  
  Purchase #5 $179.95   5.152%   $189.221   $189.22   $189.20   $189.20  
  Purchase #6 $178.77   6.155%   $189.7733   $189.77   $189.75   $189.80  
  Purchase #7 $91.29   7.718%   $98.3358   $98.34   $98.35   $98.30  
  7 purchase totals = $881.26       $943.8393   $943.84   $943.75   $943.90