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 $186.54   9.816%   $204.8508   $204.85   $204.85   $204.90  
  Purchase #2 $116.76   6.656%   $124.5315   $124.53   $124.55   $124.50  
  Purchase #3 $151.30   9.363%   $165.4662   $165.47   $165.45   $165.50  
  Purchase #4 $240.33   5.288%   $253.0387   $253.04   $253.05   $253.00  
  Purchase #5 $54.71   3.276%   $56.5023   $56.50   $56.50   $56.50  
  Purchase #6 $141.26   13.490%   $160.316   $160.32   $160.30   $160.30  
  Purchase #7 $244.60   9.277%   $267.2915   $267.29   $267.30   $267.30  
  7 purchase totals = $1,135.50       $1,231.9970   $1,232.00   $1,232.00   $1,232.00