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 $176.48   9.350%   $192.9809   $192.98   $193.00   $193.00  
  Purchase #2 $102.57   10.748%   $113.5942   $113.59   $113.60   $113.60  
  Purchase #3 $92.89   4.188%   $96.7802   $96.78   $96.80   $96.80  
  Purchase #4 $210.84   10.435%   $232.8412   $232.84   $232.85   $232.80  
  Purchase #5 $186.37   8.529%   $202.2655   $202.27   $202.25   $202.30  
  Purchase #6 $20.61   8.417%   $22.3447   $22.34   $22.35   $22.30  
  Purchase #7 $200.67   11.367%   $223.4802   $223.48   $223.50   $223.50  
  7 purchase totals = $990.43       $1,084.2869   $1,084.28   $1,084.35   $1,084.30