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 $173.49   11.740%   $193.8577   $193.86   $193.85   $193.90  
  Purchase #2 $223.39   12.181%   $250.6011   $250.60   $250.60   $250.60  
  Purchase #3 $94.50   10.158%   $104.0993   $104.10   $104.10   $104.10  
  Purchase #4 $243.61   13.270%   $275.937   $275.94   $275.95   $275.90  
  Purchase #5 $71.49   6.513%   $76.1461   $76.15   $76.15   $76.10  
  Purchase #6 $127.28   10.759%   $140.9741   $140.97   $140.95   $141.00  
  Purchase #7 $80.90   4.825%   $84.8034   $84.80   $84.80   $84.80  
  7 purchase totals = $1,014.66       $1,126.4187   $1,126.42   $1,126.40   $1,126.40