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 $65.98   3.398%   $68.222   $68.22   $68.20   $68.20  
  Purchase #2 $181.98   3.485%   $188.322   $188.32   $188.30   $188.30  
  Purchase #3 $138.52   6.666%   $147.7537   $147.75   $147.75   $147.80  
  Purchase #4 $175.86   9.772%   $193.045   $193.05   $193.05   $193.00  
  Purchase #5 $38.61   11.447%   $43.0297   $43.03   $43.05   $43.00  
  Purchase #6 $174.83   7.262%   $187.5262   $187.53   $187.55   $187.50  
  Purchase #7 $30.43   6.444%   $32.3909   $32.39   $32.40   $32.40  
  7 purchase totals = $806.21       $860.2895   $860.29   $860.30   $860.20