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 $74.95   7.205%   $80.3501   $80.35   $80.35   $80.40  
  Purchase #2 $37.45   9.572%   $41.0347   $41.03   $41.05   $41.00  
  Purchase #3 $209.78   7.510%   $225.5345   $225.53   $225.55   $225.50  
  Purchase #4 $26.49   11.172%   $29.4495   $29.45   $29.45   $29.40  
  Purchase #5 $180.64   7.720%   $194.5854   $194.59   $194.60   $194.60  
  Purchase #6 $244.95   5.469%   $258.3463   $258.35   $258.35   $258.30  
  Purchase #7 $223.84   6.170%   $237.6509   $237.65   $237.65   $237.70  
  7 purchase totals = $998.10       $1,066.9514   $1,066.95   $1,067.00   $1,066.90