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 $58.96   7.409%   $63.3283   $63.33   $63.35   $63.30  
  Purchase #2 $150.29   13.117%   $170.0035   $170.00   $170.00   $170.00  
  Purchase #3 $189.97   9.831%   $208.646   $208.65   $208.65   $208.60  
  Purchase #4 $190.87   5.431%   $201.2361   $201.24   $201.25   $201.20  
  Purchase #5 $210.74   3.603%   $218.333   $218.33   $218.35   $218.30  
  Purchase #6 $197.96   3.417%   $204.7243   $204.72   $204.70   $204.70  
  Purchase #7 $203.64   5.367%   $214.5694   $214.57   $214.55   $214.60  
  7 purchase totals = $1,202.43       $1,280.8406   $1,280.84   $1,280.85   $1,280.70