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 $201.33   12.167%   $225.8258   $225.83   $225.85   $225.80  
  Purchase #2 $181.86   11.307%   $202.4229   $202.42   $202.40   $202.40  
  Purchase #3 $63.47   9.635%   $69.5853   $69.59   $69.60   $69.60  
  Purchase #4 $194.55   7.470%   $209.0829   $209.08   $209.10   $209.10  
  Purchase #5 $64.76   9.478%   $70.898   $70.90   $70.90   $70.90  
  Purchase #6 $168.98   10.251%   $186.3021   $186.30   $186.30   $186.30  
  Purchase #7 $91.88   7.856%   $99.0981   $99.10   $99.10   $99.10  
  7 purchase totals = $966.83       $1,063.2151   $1,063.22   $1,063.25   $1,063.20