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 $84.75   13.168%   $95.9099   $95.91   $95.90   $95.90  
  Purchase #2 $42.67   6.388%   $45.3958   $45.40   $45.40   $45.40  
  Purchase #3 $50.47   12.351%   $56.7035   $56.70   $56.70   $56.70  
  Purchase #4 $184.82   9.715%   $202.7753   $202.78   $202.80   $202.80  
  Purchase #5 $114.96   6.746%   $122.7152   $122.72   $122.70   $122.70  
  Purchase #6 $110.31   7.756%   $118.8656   $118.87   $118.85   $118.90  
  Purchase #7 $83.30   10.415%   $91.9757   $91.98   $92.00   $92.00  
  7 purchase totals = $671.28       $734.3410   $734.36   $734.35   $734.40