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 $193.89   5.483%   $204.521   $204.52   $204.50   $204.50  
  Purchase #2 $201.85   13.378%   $228.8535   $228.85   $228.85   $228.90  
  Purchase #3 $67.55   10.432%   $74.5968   $74.60   $74.60   $74.60  
  Purchase #4 $145.26   12.166%   $162.9323   $162.93   $162.95   $162.90  
  Purchase #5 $53.27   6.121%   $56.5307   $56.53   $56.55   $56.50  
  Purchase #6 $28.94   10.554%   $31.9943   $31.99   $32.00   $32.00  
  Purchase #7 $14.40   6.583%   $15.348   $15.35   $15.35   $15.30  
  7 purchase totals = $705.16       $774.7766   $774.77   $774.80   $774.70