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 $120.31   8.220%   $130.1995   $130.20   $130.20   $130.20  
  Purchase #2 $220.36   6.795%   $235.3335   $235.33   $235.35   $235.30  
  Purchase #3 $88.55   3.546%   $91.69   $91.69   $91.70   $91.70  
  Purchase #4 $199.74   7.415%   $214.5507   $214.55   $214.55   $214.60  
  Purchase #5 $235.94   7.711%   $254.1333   $254.13   $254.15   $254.10  
  Purchase #6 $197.54   7.103%   $211.5713   $211.57   $211.55   $211.60  
  Purchase #7 $117.25   5.420%   $123.605   $123.61   $123.60   $123.60  
  7 purchase totals = $1,179.69       $1,261.0833   $1,261.08   $1,261.10   $1,261.10