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 $34.43   6.331%   $36.6098   $36.61   $36.60   $36.60  
  Purchase #2 $137.68   8.701%   $149.6595   $149.66   $149.65   $149.70  
  Purchase #3 $201.64   11.115%   $224.0523   $224.05   $224.05   $224.10  
  Purchase #4 $45.85   7.585%   $49.3277   $49.33   $49.35   $49.30  
  Purchase #5 $243.67   4.172%   $253.8359   $253.84   $253.85   $253.80  
  Purchase #6 $249.70   4.122%   $259.9926   $259.99   $260.00   $260.00  
  Purchase #7 $171.49   4.578%   $179.3408   $179.34   $179.35   $179.30  
  7 purchase totals = $1,084.46       $1,152.8186   $1,152.82   $1,152.85   $1,152.80