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 $63.81   10.607%   $70.5783   $70.58   $70.60   $70.60  
  Purchase #2 $15.53   10.823%   $17.2108   $17.21   $17.20   $17.20  
  Purchase #3 $227.60   3.254%   $235.0061   $235.01   $235.00   $235.00  
  Purchase #4 $162.87   5.170%   $171.2904   $171.29   $171.30   $171.30  
  Purchase #5 $228.66   6.714%   $244.0122   $244.01   $244.00   $244.00  
  Purchase #6 $167.84   9.153%   $183.2024   $183.20   $183.20   $183.20  
  Purchase #7 $109.59   3.648%   $113.5878   $113.59   $113.60   $113.60  
  7 purchase totals = $975.90       $1,034.8880   $1,034.89   $1,034.90   $1,034.90