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 $86.52   11.550%   $96.5131   $96.51   $96.50   $96.50  
  Purchase #2 $227.61   10.470%   $251.4408   $251.44   $251.45   $251.40  
  Purchase #3 $249.91   8.731%   $271.7296   $271.73   $271.75   $271.70  
  Purchase #4 $188.50   9.479%   $206.3679   $206.37   $206.35   $206.40  
  Purchase #5 $28.72   10.242%   $31.6615   $31.66   $31.65   $31.70  
  Purchase #6 $97.74   11.263%   $108.7485   $108.75   $108.75   $108.70  
  Purchase #7 $81.26   8.128%   $87.8648   $87.86   $87.85   $87.90  
  7 purchase totals = $960.26       $1,054.3262   $1,054.32   $1,054.30   $1,054.30