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 $166.36   8.591%   $180.652   $180.65   $180.65   $180.70  
  Purchase #2 $218.57   5.504%   $230.6001   $230.60   $230.60   $230.60  
  Purchase #3 $99.66   4.398%   $104.043   $104.04   $104.05   $104.00  
  Purchase #4 $185.46   4.612%   $194.0134   $194.01   $194.00   $194.00  
  Purchase #5 $11.52   4.257%   $12.0104   $12.01   $12.00   $12.00  
  Purchase #6 $216.61   3.214%   $223.5718   $223.57   $223.55   $223.60  
  Purchase #7 $80.91   9.566%   $88.6499   $88.65   $88.65   $88.60  
  7 purchase totals = $979.09       $1,033.5406   $1,033.53   $1,033.50   $1,033.50