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 $59.63   5.484%   $62.9001   $62.90   $62.90   $62.90  
  Purchase #2 $173.91   12.539%   $195.7166   $195.72   $195.70   $195.70  
  Purchase #3 $250.69   7.701%   $269.9956   $270.00   $270.00   $270.00  
  Purchase #4 $132.68   12.115%   $148.7542   $148.75   $148.75   $148.80  
  Purchase #5 $209.53   12.565%   $235.8574   $235.86   $235.85   $235.90  
  Purchase #6 $22.70   13.814%   $25.8358   $25.84   $25.85   $25.80  
  Purchase #7 $143.53   6.435%   $152.7662   $152.77   $152.75   $152.80  
  7 purchase totals = $992.67       $1,091.8259   $1,091.84   $1,091.80   $1,091.90